Asynchronous ventricular pacing: a rare cause of ventricular tachycardia.

Asynchronous cardiac pacing may induce ventricular tachycardia and fibrillation, particularly in patients with ischemic heart disease and possibly other types of myocardial abnormalities. All patients with implanted asynchronous pacemakers, and those whose demand pacemakers operate in asynchronous mode for any reason, are to be considered at risk from this complication. In patients with serious myocardial abnormalities consistent demand pacing should be assured, even if it requires early pacemaker replacement.

Reversible renal concentrating defect in shock.

The loss of renal concentrating power in haemorrhagic shock is reversible upon correction of the shock state. Shock resulting from acute hypovolaemia leads to the following sequence of events: (1) diminished renal blood-flow; (2) decreased superficial cortical nephron perfusion; (3) continued juxtamedullary nephron perfusion; (4) enhanced proximal reabsorption of Na, Cl, and H23; (5) decreased delivery of these ions to the ascending limb, which results in diminished hypertonicity of the medullary interstitium. This hypotonicity is worsened by the "washout" effect on the interstitial hypertonicity caused by continued perfusion of the juxtamedullary vasa recta which results in (6) diminished renal concentrating capacity due to elimination of medullary hypertonicity.